This invention refers to a method and an apparatus for mixing and producing multi-component plastic materials, for example polyurethane to be fed into a mould, in which components are fed simultaneously in proportioned quantities, into a limited area of a mixing chamber.
Various attempts have been made to mix three or more components in a mixing head of the high-pressure type in which the components are fed, at high pressure and in proportioned quantities, to the respective nozzles which inject them through lateral inlet apertures situated in a limited area of a mixing chamber. Said inlet apertures are usually placed opposite each other or at the sides of an imaginary plane of symmetry so that the various atomized jets of components, colliding at high speed, mix thoroughly together. The arrangement of the injection nozzles opposite each other in the mixing chamber makes it possible in general to achieve a satisfactory degree of mixing and a suitable nozzle arrangement for just two components; therefore, mixing a third component together with the others proves difficult for various reasons, depending upon the disposition of the nozzle or of the inlet aperture of said component, or upon the feeding mode of the component itself.
Therefore, it was suggested to feed a certain number of components, unable to inter-react chemically, for example, by premixing them together in a storage tank, or by introducing one component into the feeding duct of another, before injecting them into the mixing chamber. None of these solutions have ever been able to fully satisfy the need for thorough and homogenous mixing of three or more components, as they give rise to a non-homogenous mixture and the consequent moulding of articles with faulty parts, for example, due to the presence of streaking or alterations in the physical and mechanical characteristcs of the moulded article.
Therefore, an aim of this invention is to provide a method for mixing several components, in particular for moulding polyurethane, in which the mixing of a third component, such as a colouring agent, a release agent or a different type of component, is carried out by such method and means as to enable the thorough and complete simultaneous mixing of all the components, without the need for substantial and expensive modifications or addition of devices or other parts to the mixing apparatus.
A further aim of this invention is to provide a multi-component mixing apparatus, operating according to the claimed method, which makes use of a usual mixing head, designed for the simultaneous mixing of components, making use of extremely simple and inexpensive means which ensure a high degree of mixing of the third component which is fed directly into the injection area of the other components in the mixing chamber.